Here is a fun and quick tutorial that will tech you how to turn a photo into a sketch using Adobe
Photoshop. This is specifically geared towards people photos, I really haven't tried it with anything else.
First open a photo in photo shop:
I like to cut the background out so that only the person remains. Cutting the background out is beyond the scope of this tutorial, however there are several ways to do it.
Hold down the "ctrl" key and click the "U" key to open the Hue and Saturation dialog. Slide the saturation all the way to the left so that the image is black and white.
Hold down the "ctrl" key and click the "J" key to duplicate the layer of the person with the transparent background.
Select the top layer that you duplicated and go to the filter menu and select "Stylize->Find Edges"
Now make it so that the Opacity is 20%
Select the original layer, under the one you just edited, and go to the filter menu and select "Artistic->Paint Daubs". I used brush size =1 with a sharpness of 8.
The only thing that you will need to watch for is the resolution of your image. This example image was 72dpi so if you work with a hi-res photo the settings will need to be adjusted accordingly.